In this paper, the adsorption-desorption variations of trivalent La, Ce, Y and mixed rare earths are discussed. The curves of pH-rare earth element adsorption were very well fitted to the equation: InD =a+b pH. The se...In this paper, the adsorption-desorption variations of trivalent La, Ce, Y and mixed rare earths are discussed. The curves of pH-rare earth element adsorption were very well fitted to the equation: InD =a+b pH. The selectivity of RE (rare earth element) ions by the samples decreased in the following order: Ce> RE> La> Y, but the sequences were: La> Ce> Y on kaolinite and Y> La on amorphous iron oxide. Since the trivalent RE ions existed in the form of RE(OH)2+ in the solutions from pH < 5.45 to 7.0, the ratio of H+ displaced to RE3+ adsorbed in micromole was proposed to be about 2. The specific adsorption mechanism for RE was proposed to be that the RE ions complexed with oxide surface and the ion-surface complex of Ce3+ promoted oxidization on Mn hydroxide.展开更多
Understanding the adsorption and desorption behavior of methane has received considerable attention since it is one of the crucial aspects of the exploitation of shale gas.Unexpectedly,obvious hysteresis is observed f...Understanding the adsorption and desorption behavior of methane has received considerable attention since it is one of the crucial aspects of the exploitation of shale gas.Unexpectedly,obvious hysteresis is observed from the ideally reversible physical sorption of methane in some experiments.However,the underlying mechanism still remains an open problem.In this study,Monte Carlo(MC) and molecular dynamics(MD) simulations are carried out to explore the molecular mechanisms of adsorption/desorption hysteresis.First,a detailed analysis about the capillary condensation of methane in micropores is presented.The influence of pore width,surface strength,and temperature on the hysteresis loop is further investigated.It is found that a disappearance of hysteresis occurs above a temperature threshold.Combined with the phase diagram of methane,we explicitly point out that capillary condensation is inapplicable for the hysteresis of shale gas under normal temperature conditions.Second,a new mechanism,variation of pore throat size,is proposed and studied.For methane to pass through the throat,a certain energy is required due to the repulsive interaction.The required energy increases with shrinkage of the throat,such that the originally adsorbed methane cannot escape through the narrowed throat.These trapped methane molecules account for the hysteresis.Furthermore,the hysteresis loop is found to increase with the increasing pressure and decreasing temperature.We suggest that the variation of pore throat size can explain the adsorption/desorption hysteresis of shale gas.Our conclusions and findings are of great significance for guiding the efficient exploitation of shale gas.展开更多
文摘In this paper, the adsorption-desorption variations of trivalent La, Ce, Y and mixed rare earths are discussed. The curves of pH-rare earth element adsorption were very well fitted to the equation: InD =a+b pH. The selectivity of RE (rare earth element) ions by the samples decreased in the following order: Ce> RE> La> Y, but the sequences were: La> Ce> Y on kaolinite and Y> La on amorphous iron oxide. Since the trivalent RE ions existed in the form of RE(OH)2+ in the solutions from pH < 5.45 to 7.0, the ratio of H+ displaced to RE3+ adsorbed in micromole was proposed to be about 2. The specific adsorption mechanism for RE was proposed to be that the RE ions complexed with oxide surface and the ion-surface complex of Ce3+ promoted oxidization on Mn hydroxide.
基金supported by the National Natural Science Foundation of China(Grant Nos.11525211,and 11472263)the CNPC-CAS Strategic Cooperation Research Program(Grant No.2015A-4812)+1 种基金Anhui Provincial Natural Science Foundation(Grant No.1408085J08)the Fundamental Research Funds for the Central Universities of China
文摘Understanding the adsorption and desorption behavior of methane has received considerable attention since it is one of the crucial aspects of the exploitation of shale gas.Unexpectedly,obvious hysteresis is observed from the ideally reversible physical sorption of methane in some experiments.However,the underlying mechanism still remains an open problem.In this study,Monte Carlo(MC) and molecular dynamics(MD) simulations are carried out to explore the molecular mechanisms of adsorption/desorption hysteresis.First,a detailed analysis about the capillary condensation of methane in micropores is presented.The influence of pore width,surface strength,and temperature on the hysteresis loop is further investigated.It is found that a disappearance of hysteresis occurs above a temperature threshold.Combined with the phase diagram of methane,we explicitly point out that capillary condensation is inapplicable for the hysteresis of shale gas under normal temperature conditions.Second,a new mechanism,variation of pore throat size,is proposed and studied.For methane to pass through the throat,a certain energy is required due to the repulsive interaction.The required energy increases with shrinkage of the throat,such that the originally adsorbed methane cannot escape through the narrowed throat.These trapped methane molecules account for the hysteresis.Furthermore,the hysteresis loop is found to increase with the increasing pressure and decreasing temperature.We suggest that the variation of pore throat size can explain the adsorption/desorption hysteresis of shale gas.Our conclusions and findings are of great significance for guiding the efficient exploitation of shale gas.
